1. Field
One or more embodiments relate to wellbore flow diversion tools, and more particularly, to a wellbore flow diversion tool utilizing tortuous paths in a bow spring centralizer structure.
2. Description of the Related Art
Virtually every well drilled in shale experiences production decline, largely due to the limited effectiveness of methods by which the source rock (shale) is hydraulically fractured (frac'd) in an effort to provide channels for the oil to flow to the well bore. The future of the oil industry will rely heavily on the ability to re-stimulate sections of horizontal shale oil wells which have already been drilled and stimulated (frac'd) during the wells' completion phase. In virtually every case, steel pipe (parent pipe) lines the open bore hole for stability and it is permanently in place, stuck by sand or cemented from the initial completion of the well.
In many cases after oil production in a well has depleted, the well can be partially or possibly fully restored to original completion oil production levels by re-frac'ing the well bore. If done correctly, this is like getting two oil wells for the price of one, and represents a large cost savings compared to drilling an entirely new oil well. In some instances, a parent pipe has been broken from stress or eroded from frac sand, and has lost pressure integrity. Many wells have not been completed because in early stages the parent pipe (usually at the heel of the well) has failed and frac'ing operations have been halted, leaving much of the well in an uncompleted stage.
How the well was completed initially impacts the ability to restore the well to completion oil production levels. Steel pipe lines the well bore from surface to total depth. This pipe has to be perforated via a “plug ‘n’ shoot” process or windowed using frac sleeves which are installed in-line on the pipe at intervals where the frac is to be performed. This allows multiple sections of the well bore to be frac'd individually, starting at the toe (bottom) of the well and working up to the curve (heel) of the well. Fifty sections (stages) are not uncommon in a well. Prior to production, a drill bit is run through the steel pipe to clean out the composite plugs or frac sleeve remnants and all of the stages are produced together.
Common sense would indicate that the entire well bore could be treated in one big frac stage, but in practice, many small stages are the only means of controlling the direction, height, and frac fluid volume along the well bore. To re-frac the existing open sections of the pipe, a method is needed to again isolate the open sections from each other and start frac'ing over again from the toe to the heel.
There have been different methods proposed to pressure-isolate sections of the well while individual sections are being re-stimulated at high pressures and flow rates. One method is to use chemicals or cement pumped into the existing holes or windows in the pipe in an effort to plug them. This is expensive and considered high risk in terms of having confidence that the holes or windows are adequately plugged.
Another method is to insert and run a pipe (tubing) barely smaller than the parent pipe into the parent pipe. The tubing includes tools on the end of it that seal the inside of the pipe and straddle the intervals where frac'ing had been performed. Each interval is re-frac'd through the tubing. The tools have inner diameter restrictions which limit the rate of frac fluid injection, which is critical to establish and maintain a fracture in the shale, and present a risk of getting the tools stuck with frac sand.
Other methods include cementing the tubing in place after inserting the tubing barely smaller than the parent pipe into the parent pipe, which has had poor results, or placing isolation devices on the outside of the smaller pipe which seal against the inside of the parent pipe. The isolation devices then contain pressure between them as the zone between them is re-stimulated or frac'd. Fluids used to stimulate may include acids, gels, gases, solvents, etc. Legacy technology exists to seal off the annulus between the larger and smaller pipes at measured intervals using elastomers; however, very thin cross sections of elastomers needed to provide a reasonably large diameter in the smaller pipe have proven to be weak and unreliable. Also, due to the very close inner diameter/outer diameter dimensions, the general practice with elastomers requires downsizing the diameter of the smaller pipe. This creates an unacceptable pressure drop for re-stimulation, especially considering that the smaller pipe will vary in length from one to two and a half miles into the horizontal section of the parent pipe. Wells also have a large volume of debris like sand, cast iron, or fiberglass, which can cause attempts to achieve setting depths with the smaller pipe to fail. In addition, some designs using elastomers in hydraulic set packers require severely restricting the inner diameter of the tubing at the packers and creating bottlenecks, which would be too small for passing composite plugs and perforating guns in the “plug ‘n’ perf” re-frac method. Another technique using elastomers includes mounting a swellable elastomer between tubing and a parent casing to seal off a section inside of the parent casing. The swellable elastomer swells up in combinations of water or oil-based fluids. In particular applications, e.g., vertical wells, fluid levels are very low and fluid necessary to swell the elastomers is absent. Also, in the vertical and low fluid level wells, a large inner diameter is typically required in order to run production pumps deep enough to reach the oil level.